Sec. 6. If, in the opinion of the Factory Inspector, or of the Assistant Factory Inspector, or of a Deputy Factory Inspector, it is necessary to insure the safety of the persons employed in any manufacturing establishment, three or more stories in height, one or more fire-escapes, as may be deemed by the Factory Inspector as necessary and sufficient therefor, shall be provided on the outside of such establishment, connecting with each floor above the first, well fastened and secured and of sufficient strength, each of which fire-escapes shall have landings or balconies, not less than six feet in length and three feet in width, guarded by iron railings not less than three feet in height, and embracing at least two windows at each story and connecting with the interior by easily accessible and unobstructed openings, and the balconies or landings shall be connected by iron stairs, not less than eighteen inches wide, the steps not to be less than six inches tread, placed at a proper slant, and protected by a well-secured hand-rail on both sides with a twelve-inch-wide drop-ladder from the lower platform reaching to the ground. Any other plan or style of fire-escape shall be sufficient, if approved by the Factory Inspector; but if not so approved, the Factory Inspector may notify the owner, proprietor, or lessee of such establishment or of the building in which such establishment is conducted, or the agent or superintendent or either of them, in writing, that any such other plan or style of fire-escape is not sufficient, and may, by an order in writing, served in like manner, require one or more fire-escapes, as he shall deem necessary and sufficient, to be provided for such establishment, at such locations and of such plan and style as shall be specified in such written order. Within twenty days after the service of such order, the number of fire-escapes required in such order for such establishment shall be provided therefor, each of which shall be either of the plan and style and in accordance with the specifications in said order required, or of the plan and style in this section above described and declared to be sufficient. The windows or doors to each fire-escape shall be of sufficient size, and be located as far as possible consistent with accessibility, from the stairways and elevator hatchways or openings, and the ladder thereof shall extend to the roof. Stationary stairs or ladders shall be provided on the inside of such establishment from the upper story to the roof, as a means of escape in case of fire.